GEOLOGY AND PALEONTOLOGY OF THE CANAL ZONE. 311 



marine tuffs. The most recent movements have been differential, and while uplift 

 has taken place at the southeastern side of the island, subsidence has occurred to the 

 east and north. The modern barrier reef occurs where subsidence has taken place 

 either due to tilting or faulting during uplift.^ 



Concerning the Lau Islands, he states: 



Within quite recent times the islands have subsided 50 to 90 feet and the modern 

 coral reefs are developing on the eroded and submerged platforms.* 



One paragraph of Foye's conclusions is as follows: 



The data assembled by Daly and Vaughan convince the writer that Pleistocene 

 platforms exist very generally throughout the coral seas. Yet while this is true, the 

 platforms in Fiji are post-Pleistocene in their development. The writer was unable 

 to discover any evidence of Pleistocene wave-cut platforms. ^ 



The second one of Foye's papers * contains the following signifi- 

 cant statement: 



There is another method by which atolls develop. The limestone islands are rapidly 

 eroded to sea level by atmospheric solution. Evidence of this process may be seen 

 in the diminishing limestone masses within the lagoons of many of the Lau islands. 

 By tidal scour and wave action platforms are developed slightly below sea level. 

 Examples of such platforms may be seen about Fulanga and Ongea. It is significant, 

 however, that most of these islands have lagoons 10 to 15 fathoms in depth. Such 

 depths can not be ascribed to erosion, but miist be the result of recent submer- 

 gence. * * * 



The information bearing on the Fijis may be summarized as fol- 

 lows: 



1. The fringing reefs have unconformable' basal contacts, as do 

 those of the West Indies. 



2. The barrier reefs are superposed on antecedent platforms of 

 diverse origin during or after submergence. 



3. The submergence is concomitant with, if not actually due to, 

 differential crustal movement. 



4. In that they were formed during or after submergence and are 

 superposed on antecedent platforms, the offshore reefs of the Fijis 

 accord with all others, perhaps except a Barbadian reef, so far 

 considered. 



SOCIETY ISLANDS. 



TAHITI. 



That Tahiti had undergone subsidence is implied in statements by 

 Dana,^ the occasional harbors being mentioned in two places in his 

 book. W. M. Davis says:" 



The cliff -rimmed island of Tahiti, the largest and youngest of the group, has suffered 

 moderate subsidence after its cliffs were cut, but its bays are now nearly all filled 

 with delta plains; hence a pause or stillstand has followed its latest sinking. 



1 The geology of the Fiji Islands, Acad. Nat. Sci. Proc, p. 308, April, 1917. 



2 Idem, p. 309. 



3 Idem, p. 309, 310. 



* Foye, W. G., The geology of the Lau Islands, Amer. Joum. Sci., ser. 4, vol. 43, pp. 343-350, May, 1917. 

 6 Corals and coral islands, ed. 3, pp. 149, 158, 246, 247, 1890. 

 6 Amor. Journ. Sci., ser. 4, vol. 40, p. 271, 1915. 



37149— 19— Bull. 103 9 



